This invention relates to a premix storage hopper for storing a paste-like or slurry-like viscous mixture containing cellulose dispersed in a solvent therefor. In particular the viscous mixture is maintained in a workable condition within the storage hopper prior to being pumped to a dope forming system in which the mixture is subjected to elevated pressure and an increased temperature to cause the cellulose to dissolve in the solvent so as to produce a viscous cellulose dope suitable for spinning or extruding. The invention also relates to a method of storing such a viscous mixture in a workable condition after formation of the mixture and prior to conveying the mixture to a dope forming stage.
In McCorsley et al U.S. Pat. No. 4,211,574, McCorsley et al U.S. Pat. No. 4,142,913 and McCorsley U.S. Pat. No. 4,144,080 there are disclosed methods of forming solid precursors of solutions of cellulose in amine oxide. In each of these known methods, cellulose is suspended in a mixture at an elevated temperature which is a non-solvent for the cellulose at the temperature of the suspension and which contains tertiary amine oxide and water. The mixture is allowed to cool to ambient room temperature and the resulting solid product is comminuted into chips. These solid chips can be stored until required when they are subjected to elevated temperature and pressure to convert the mixture into a viscous liquid in which the cellulose is dissolved in the amine oxide solution to form a cellulose dope suitable for spinning or the like.
In McCorsley U.S. Pat. No. 4,416,698 there is disclosed a method of forming a cellulose dope by mixing at elevated temperature and pressure ground cellulose and tertiary amine N-oxide in a barrel of an extruder screw prior to extruding the formed cellulose dope to form a shaped cellulose product. This patent specification also refers to the possibility of premixing the cellulose and tertiary amine N-oxide at elevated temperatures and pressures to form a cellulose dope prior to conveying the mixture to the extruder.
As far as we are aware it is not known to form a viscous premix of cellulose dispersed in a solvent therefor and to store the premix in its viscous condition prior to conveying the premix to a subsequent cellulose dope forming stage.